Modelling and the Experimental Validation of the Long-term Averaged Solar Radiation on a Tilted Solar Collector Facing the South-East Direction

The paper shows the modelling and its experimental validation of the monthly averaged daily radiation on the tilted south-east facing surface of a solar collector, which is the collecting component of a solar water heating system situated in a location utilized as the case study. The modelling is based on the general form of the "Klein and Theilacker method". To perform the calculation of the monthly averaged clearness index for the case study, one of the available models is utilized Monthly averaged values of the ratio of total radiation on a sloped surface to that on a horizontal one are determined. Also, the monthly averaged values of daily radiation on the sloped surface are estimated. Validation of the estimated values through the application of the "Klein and Theilacker method" is performed based on recorded experimental data obtained every minute during a multiyear period. Some statistical parameters utilized in this work include the percentage error, the mean bias error, the mean percentage error, the root mean square error, and the coefficient of determination. The comparison of predicted and experimental data confirms the ability of the utilized method for the considered tilted south-east facing surface and location. It is noticed that the method slightly overestimates the measured values during the winter season.